Residents along Australia's east coast awoke today morning to a seemingly portentous orange, glowing sky as winds swept millions of tonnes of red dust from the country's drought-ravaged interior and dumped it on Sydney.

The city's opera house turned orange, flights at Sydney and Brisbane airports were delayed, building sites shut down, people choked on dust, and emergency departments were flooded with calls as the worst dust storm to hit Australia in 70 years darkened the skies.

The country's meteorology office said the storm carried 10 times the particle pollution than the previous record and that overall air pollution was 1,500 times normal levels. It predicted another storm would hit in the next day or two.

Health officials urged people to stay inside as Sydney's air was expected to remain choked with particles for up to three more days.

Dr John Leys, principal research scientist with the New South Wales department of climate change and water, told the Sydney Morning Herald that initial estimates showed the dust plume stretched 373 miles along the state's coast from Sydney to the Queensland border, dumping up to 75,000 tonnes of dust an hour into the Tasman Sea. "It's travelled about 1,500km to get to Sydney," he said.

Residents reacted with a mixture of awe and fear. "It did feel like Armageddon because when I was in the kitchen looking out the skylight, there was this red glow coming through," one resident told ABC radio.

Sydney was one of the top 10 most popular topics on Twitter today, as the city's skyline and landscape was variously likened to Mars, the aftermath of an alien attack and judgment day. Many people rushed to share their photographs online.

"Apocalyptic marsscape from Katoomba down to the Sydney basin today. Amazingly red at first light this morning," 13264u twittered.

Another Tweeter, francescaway, said: "Felt blessed to witness the legendary duststorm, even if it meant feeling like breathing sawdust all day."

Many people suffered breathing difficulties. Some wore masks, others wrapped their faces in scarves or pressed cloths over their noses and mouths and the emergency services were inundated by phone calls.

The state ambulance service said it had received more than 250 calls before midday from people suffering breathing problems and the fire service received more than 500 calls between 3am and 7am as alarms were set off by the dust. Flights were diverted from Sydney airport, where visibility was down to 400 metres, and ferries on the city's famous harbour were suspended. Building sites were shut down.

The dust over Sydney had largely cleared by mid-afternoon. But the storm – which reduced visibility to 100 metres in some areas – was part of a series of freak weather conditions that battered Australia: heavy rains lashed Adelaide in the south, where streets flooded.

Then as morning dawned two tremors shook Melbourne. Later in the day hailstones as big as cricket balls pelted parts of New South Wales.

In Queensland, firefighters battled a string of blazes as the unseasonally dry weather stoked the flames.